Mexico City: Three men who had worked as news photographers were found slain and dumped together in plastic bags by a canal in the eastern Mexico state of Veracruz, less than a week after the killing in the same state of a reporter for an investigative newsmagazine, officials and colleagues said.

Press advocates called for immediate government action to halt a wave of attacks that has killed at least six current and former reporters and photographers in Veracruz over the last year, most of them among the few journalists still working on crime-related stories in the state.

The Thursday’s deaths have spawned an atmosphere of terror and self-censorship among journalists.

The problem isn't confined to Veracruz. Mexico is one of the world's most dangerous countries for journalists, with reporters and photographers suffering a rising number of attacks in recent years as the country grapples with tens of thousands of killings, kidnappings and extortion against the backdrop of a militarised government offensive against drug cartels.

Prosecutions in the cases are all but unknown, as is the case with almost all homicides and other serious crimes in Mexico.

The latest killings came in Boca del Rio, a town near the port city of Veracruz where police found the dismembered bodies of four people on Thursday, the Veracruz state Attorney General's Office said.

One victim was identified as Guillermo Luna Varela, photographer for a news website. Another was identified as Gabriel Huge, who the director of the website said had been working as a photojournalist in the area. State officials said the third victim was Esteban Rodriguez, who was a local newspaper photographer until last year, when he quit to work as a welder. The fourth victim was Luna's girlfriend, Irasema Becerra, state prosecutors said.

State officials said the killings bore the hallmarks of organised crime and they would ask federal authorities to help investigate.

The bodies were found after passers-by spotted four suspicious black plastic bags near a wastewater canal, five days after the discovery of the corpse of Regina Martinez, a correspondent for the national magazine Proceso who often wrote about drug trafficking.